Gel production from plant matter

ABSTRACT

A method of producing a gel material and which comprises firstly providing an aqueous soluble hemicellulosic starting medium which is free of glucans and obtainable from testaceous plant material. The starting medium is then extracted with a non-acidic reagent and reacted with an oxidizing system comprising at least one peroxide, together with at least one oxygenase (such as a peroxidase). 
     A gel material which is obtainable from a hemicellulosic starting medium, and which is substantially free of glucans and pectins. The gel material comprises a polysaccharide network for a matrix of polysaccharide chain segments and a multiplicity of cross-linking ferulate bridges. The ferulate bridges are located at regular intervals along the cross-linked segments.

The present invention is concerned with the production of gels fromplant matter and the resulting gels.

Large numbers of plant sources contain hemicelluloses, which arecomposed of various arrangements of pentoses (such as xylose andarabinose), hexoses (such as mannose, glucose and galactose) and/oruronic acids (such as glucuronic and galacturonic acid). Examples ofhemicellulosic materials include xylans (such as arabinoxylan), mannansand galactans, which may be substituted by phenolic acid residues suchas ferulic acid (4-hydroxy-3-methoxycinnamic acid), coumaric acid(p-hydroxycinnamic acid) or vanillic acid (4-hydroxy-3-methoxyl benzoicacid). Such materials occur naturally in cereals such as maize, barley(including malted barley), wheat, oats and rice; pulses, such as soya;legumes and fruit.

French patent specification 2545101 is concerned with modification ofsugar beet pectins by reacting an oxidising system comprising an enzyme(such as peroxidase) and an oxidising agent (such as hydrogen peroxide)with pectins which have been isolated from sugar beet. The isolation ofpectin comprises subjecting the sugar beet to acidic extraction and heattreatment.

According to the present invention, there is provided a method ofproducing a gel material, which method comprises:

(a) providing an aqueous soluble hemicellulosic starting medium which issubstantially free of glucans and is obtainable from testaceous plantmaterial;

(b) extracting said starting medium with a non-acidic aqueous reagent;and

(c) reacting the extracted material with an oxidising system comprisingat least one peroxide, together with at least one oxygenase (such as aperoxidase).

The soluble hemicellulosic starting medium is typically prepared fromwaste testaceous plant material containing a significant quantity (suchas at least about 10%, such as about 20%) of arabinoxylan orglucuronoarabinoxylan, which is present in nature primarily in the cellwall regions. Examples of preferred such sources include waste materialswhich are rich in cell walls, such as cereal husk or bran, or legumes(pulses). Typical cereal husk or bran includes maize, barley, wheat,rice or oats, or malt or malt culms (dried germinated barley rootlets).

In a preferred embodiment, the hemicellulosic starting medium is in asubstantially ground form having a particle size of not more than about100 microns. The plant material is therefore typically ground, either indry or wet form (such as milling or wet grinding known as maceration) tothe required particle size. The ground material is typically airclassified or sieved to remove starch. The method may comprise starchremoval by suitable enzyme treatment, for example, with diatase (alphaand/or beta-amylase).

The glucans are preferably removed from the plant material by enzymedigestion with carbohydrase enzymes such as glucanase.

The insoluble enzyme treated material may then be dried (in air) beforefurther processing. The plant material may have been pre-treated so asto remove the glucans prior to application of the present method, but itis preferred that the method according to the invention involves enzymetreatment so as to remove glucans following the above described grindingof the plant material.

Suitable glucanases for use according to the invention are commerciallyavailable under the trade marks Viscozyme, Biofeed and Biofeed Pluswhich typically also have hemicellulase, cellulase, arabinase andxylanase activity. Viscozyme is currently preferred.

The non-acidic extraction preferably comprises treatment with hot wateror weak alkali typically of less than 0.5% by weight of the aqueousreagent. Preferred alkalies are NaOH and KOH. The alkali is preferablyused in an amount of 0.1 to 10% (typically 0.5 to 2.5%) by weight of theaqueous reagent, for times of from 20 minutes to 5 hours (typicallyabout 2 hours) Alternatively, gel may be produced from wheat bran andbarley dust or culms by using hot water in place of alkali.

The alkaline extraction may be at a temperature of from 30° to 100° C.and is typically at a temperature of 60° to 90° C. generally for 10minutes to 5 hours. For strong gels, temperatures of 60° to 75° C. arepreferably used for 0.5 to 1.5 hours; for weaker gels temperatures of6020 to 85° C. are preferably used for 2 to 5 hours. Hot waterextraction is carried out at temperatures of 50° to 80° C. (typically60° to 70° C.) for 0.5 to 2 hours (typically 1 to 1.5 hours). Theextraction is generally effected with gentle stirring. The resultingextracted material generally comprises insoluble cellulose and solublehemicelluloses; the cellulose is typically removed by centrifugation,either with or without acidification.

It is advantageous to avoid extreme conditions (such as sustainedcontact of the hemicellulosic medium with sodium hydroxide ortemperatures above the above-described preferred range) during alkalineextraction in order to optimise the gelling characteristics of gelmaterial produced by a method according to the present invention.

Alkaline extraction will produce an extracted material substantiallyfree of pectins as the latter are labile in alkaline conditions and areextractable by acidic reagents as described in FR 2545101.

Following alkaline extraction the hemicellulosic material, which is richin arabinoxylans and is substituted by phenolic acids, is preferablyneutralised (for example, using hydrochloric, sulphuric, acetic orcitric acid, of which citric acid is preferred). Neutralisation isadvantageous in that it helps to preclude rapid hydrolysis of ferulicacid residues present in the extracted material; such hydrolysis woulddamage the gelling properties of the material. The solids can be removedfrom the neutralised extract by filtration or centrifugation whichresults in improved gel properties.

Purification of the hemicellulosic material may then be carried out beprecipitation with an alcohol such as methanol or ethanol (or industrialmethylated spirit), or iso-propanol (propan-2-ol). Such alcohols may beadded in amounts of from 1.5 to 3.5 volumes according to the fractiondesired by molecular weight. The hemicellulosic material mayalternatively be purified by passage through an activated carbon columnand subsequently concentrated by precipitation with ammonium sulphate at70-80% saturation or any of the above alcohols used for precipitation.Alternatively the concentration of the eluate may involve drying (suchspray or vacuum rotary drying) and redissolving of the eluate.

The hemicellulosic material may be further purified by ion-exchangetreatment, preferably with a cation exchange resin to remove cationicimpurities.

Differential precipitation or selection by molecular weight cut-off(e.g. diafiltration or cross-flow filtration) at this stage can providefractions of the polysaccharide which vary in molecular weight andexhibit different rheological properties and consequently viscoelasticproperties of the gels they produce. For example precipitation withammonium sulphate at saturations of between 60 and 80% yields fractionsdiffering in molecular weight; similarly addition of ethanol of 1.7 to 3volumes yields the same range of fractions.

After separation by filtration or centrifugation, and redissolving ofthe precipitate in water, a second precipitation may be carried out byaddition of 2 to 4 volumes of alcohol. The fraction obtained may befiltered (and dried on the filter using ether) or redissolved in waterand lyophilised.

The salt content may be lowered if wished (for example, if the final gelis to be used in foodstuffs), typically by dialysis or tangential flowultrafiltration. The de-salted material may be separated on an anionexchange resin such as Purolite A500 to produce fractions differing incharge (dependent on uronic acid content). Selection of fractions atthis stage can further control the rheological/viscoelastic propertiesof the final product. The resulting material may be dried (for example,by spray drying, freeze drying, vacuum rotary drying or drying on afilter using diethyl ether) at this stage; the resulting dried materialmay be rehydrated prior to treatment with an oxidising system asdescribed below.

The rehydrated material (or, if relevant, the non-dried material) isthen treated with a peroxide (such as H₂ O₂) and a peroxidase (such ashorseradish peroxidase). By varying the hydrogen peroxide concentration,and hence the number of free ferulic acid groups that become di-feruliccross links, the extent of cross-linking within the resulting gel can becontrolled. For example, a 0.5% solution of the hemicellulosic startingmedium may produce gels with "hardness" varying from 0.008 kg to 0.058kg by adjusting the concentration of hydrogen peroxide in the enzymicreaction. The term "hardness" is a measure of the viscoelasticproperties of the gel.

The gel properties may be further modified by the conditions used inperoxidase treatment. The treatment with a peroxidase (with a smallamount of the peroxide) can result in a weak to strong clear gel atconcentrations of 0.05 to 10% (preferably 0.5 to 2.5%). The balance isgenerally water. Polyvalent metal cations (such as Ca²⁺, Cu²⁺, Zn²⁺,Fe³⁺ or Al³⁺) added prior to peroxide/peroxidase treatment will modifythe gels, for example such that they can subsequently break into sols.

In any case, the resulting gel, which is constituted of cross-linkedfibrous material comprising a phenolic acid substituted polysaccharidenetwork, typically rich in arabinoxylans, is highly thermostable and maybe autoclaved. (For example, the gel may withstand 15 psi at 122° C. for15 minutes). The purified gels in particular can be made withreproducible viscoelastic and rheological properties.

Further control over the viscoelastic properties (such as brittleness)may be exercised by addition of sugar, salts or alcohols, or bytreatment with carbohydrase enzymes.

The peroxidase is typically used in an amount of 1 to 100 micrograms pergram of substrate; the peroxide is typically used in an amount of theorder of one tenth of the amount of peroxidase.

According to a first aspect of the present invention, there is provideda gel material obtainable from a hemicellulosic starting medium, saidgel material being substantially free of glucans and pectins andcomprising a polysaccharide network which comprises:

(i) a matrix of polysaccharide chain segments; and

(ii) a multiplicity of cross-linking ferulate bridges disposed atbonding locations at substantially regular intervals along cross-linkedsegments.

The gel material according to the first aspect of the present inventionis characterised by infra-red absorbance both in the wavelength range of1550-1600 cm⁻¹ and in the wavelength range of 1100-1160 cm⁻¹.

According to a second aspect of the present invention, there is provideda gel material obtainable from a hemicellulosic starting medium, saidmaterial comprising a polysaccharide matrix having a substantiallyregular array of cross-linking bridges and being characterised byinfra-red absorbance both in the wavelength range of 1550-1600 cm⁻¹ andin the wavelength range of 1100-1160 cm⁻¹.

The gel material according to the second aspect of the present inventionis preferably substantially free of glucans and pectins. The absence ofthese relatively large sugar units facilitates the formation ofcross-linking bridges within the polysaccharide matrix.

The polysaccharide matrix preferably comprises a multiplicity ofpolysaccharide chain segments joined by means of the cross-linkingbridges. The regular array of cross-linking bridges typically consistsessentially of ferulate bridges disposed at bonding locations atsubstantially regular intervals along the chain segments of thepolysaccharide matrix. The ferulate moieties are responsible for thecharacteristic infra-red absorbance both in the wavelength range of1550-1600 cm⁻¹ and in the wavelength range of 1100-1160 cm⁻¹ exhibitedby the gel material.

The frequency of ferulate bridges within the polysaccharide networkinfluences the properties of the resulting gel. As described above, theextent of ferulate cross-linking can be substantially controlled byselected reaction conditions during treatment with the peroxide andoxygenase, wherein ferulic acid residues are oxidatively coupled to formthe di-ferulate cross-links.

A gel material provided with a substantially regular arrangement offerulate bridges as described above closely approximates an "ideal gelsystem". The term "ideal gel system" as used herein denotes a gel ofsubstantially ordered macromelecular structure, the production of whichis desirable due to the substantially predictable properties of theresultant gel.

A gel according to the present invention is preferably obtained from ahemicellulosic starting medium according to a method substantially ashereinbefore described. The present invention therefore allows theproduction of an ideal gel system from a naturally occurring biologicalmaterial. The above definition of a gel according to the presentinvention also encompasses a gel material obtained by chemical synthesistechniques.

It is preferred that the polysaccharide network comprises a plurality ofdiscrete polysaccharide chains linked by means of the ferulate bridges.The polysaccharide chain segments are preferably rich in arabinoxylan orglucuronoarabinoxylan moieties. Typically, the molecular integrity ofthe arabinoxylan or glucuronoarabinoxylan moieties is substantiallydisrupted as a result of enzyme treatment of the hemicellulosic startingmedium. As hereinbefore described, the enzyme treatment typicallyinvolves treatment by suitable glucanases, such as glucanasescommercially available under the trade marks Viscozyme, Biofeed andBiofeed Plus.

The gel material may further comprise an aqueous liquid, such as water,which is preferably present in an amount of 98-99.9% by weight. Theremay further be present in the gel material metal cations as hereinbeforedescribed.

The molecular weight of the gel material according to the presentinvention is typically in the range of 80 to 600 kdaltons (moregenerally 90 to 500 kdaltons).

There is further provided by the present invention a gel materialobtained by a method substantially as hereinbefore described.

Viscous solutions rather than gels can be produced by either furtherlimitation of the peroxide concentration or by using a solution having ahemicellulosic concentration below the critical gel-formingconcentration of about 0.05%. For example, solutions of viscosityvarying between 100 and 500 cP may be produced from a 0.1%hemicellulosic concentration by limiting the peroxide concentration tolevels below those which form gels.

An extract produced substantially as hereinbefore described may co-gelwith other hemicellulosic-derived materials in such a way that the twogelling agents are synergistic. For example, extract material derivedfrom maize in the method according to the invention may be blended withextract material derived from other cereals (such as wheat, malt orbarley) in the method according to the invention, in proportions inwhich neither would form a firm gel along, but a firm gel is formed withthe two materials. For example, a firm gel can be obtained with 0.7 to3% of material derived from maize and about 2% of material derived fromwheat (all the above proportions being on a solids basis).

The gel material according to the invention may have a wide variety ofuses, of which the following are exemplary:

1. In medicinal compositions for example as a topical formulation orwound dressing (such as for treatment of burns) or debriding agent, as acarrier for iron or zinc, as a lubricant, or a thickener for parenteralcompositions, or as an encapsulating agent, or as a slow release vehiclefor drug delivery (either for oral, parenteral or anal delivery), or foruse for implants and prosthesis purposes for orthopaedic purposes (suchas pressure-relief gels), for ocular purposes or suppository uses. Aparticularly preferred medicinal application of the gel is for use as awound dressing, and there is further provided by the present invention awound dressing having a surface contact region comprising a gel ashereinbefore described. Advantageously, the wound dressing consistsessentially of a gel material substantially as hereinbefore described.

2. In foodstuffs or animal feeds, for example, as a cold setting gel foruse as a stabiliser for ice cream or the like, as a suspending agent forparticles such as coconut, as a glazing agent for meat or the like, as asetting agent for jams, or a thickening agent for gravies, purees,sweets, soups or the like, as a soluble fibre, as a food lubricant, as aviscosity agent for flavours, as a canning gel, functional food or fishbait.

3. In the oil industry, for example, for sealing strata above oildeposits, as an oil drilling sealing agent, as an additive to drillingmuds or the like, and for recovery of oil from oil-bearing strata.

4. In the microbiological industry, for example as a gelling agent, aspore biocontainer or a culture biocontainer.

5. In the agricultural industry, as a slow release pesticidebiocontainer, a plant culture medium, an anti-drying agent, a silage pitsealing material, or the like.

Gels obtained according to the invention may be prepared such that theyeventually break down to the sol form.

The present invention is further illustrated by reference to thefollowing Examples and accompanying drawings which do not limit thescope of the invention in any way.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphic comparison of the hardness, elasticity andbrittleness properties of a gel according to the present invention(identified as G. B. Gel), a pectin gel and gelatin;

FIG. 2 illustrates the variation of elasticity and brittleness withpolysaccharide concentration of a gel according to the presentinvention;

FIG. 3 illustrates the variation of hardness and adhesiveness withpolysaccharide concentration of a gel according to the presentinvention;

FIGS. 4a and 4b illustrate the UV spectra of (i) a ferulic acid solution(FIG. 4a), and (ii) a gel according to the present invention (FIG. 4b);

FIG. 5 is a UV reference spectra from which the extent of diferulatecross-linking in a gel according to the present invention can beestimated; and

FIGS. 6a and 6b illustrate IR spectra of (i) an ungelled polysaccharide(FIG. 6a), and (ii) a gel according to the present invention (FIG. 6b).

EXAMPLE 1

Production of a Firm Gel from Corn (Zea mays)

1. Grinding

Corn bran was subjected to grinding which involved initial wet millingfollowed by dry milling to an average particle size in the range of80-300 microns.

2. Enzyme Treatment

0.01% w/w of a cytase enzyme at 45° C. for 2 to 24 hours depending on araw material type and textures (e.g. for milled corn bran a period ofabout 6 hours).

3. Alkali Extraction

A 10% (w/v) suspension of the milled corn bran in 1% w/v potassiumhydroxide (aqueous) was prepared and gently stirred at 65°-80° C. for2-3 hours.

4. Separation

The insoluble material, consisting mainly of cellulose, was removed bycentrifugation at 2500 rpm.

5. Neutralisation/Dialysis

The supernatant was carefully decanted, neutralised with hydrochloricacid (or citric acid) and dialysed against running tap water for 2 days.

6. Gelling

The concentration of the dialysed extract was adjusted to 3% w/v withdeionised water. 100 ml of this solution was taken and 1 ml of 100micrograms/ml horseradish peroxidase mixed in thoroughly. Whendistributed, 0.5 ml of hydrogen peroxide at 40 micrograms H₂ O₂ /ml wasadded and mixed in; the mixture was then left to set at ambienttemperature (5-15 min) or at a higher temperature (1-2 min at 40° C.).

An Instron Texture Profile Analyser was used to measure the hardness,brittleness and elasticity of the following:--a gel produced by theabove example, gelatin and a pectin gel cross-linked with diferulic acidwhich was prepared according to the teaching of French patentspecification 2545101.

As can be seen from FIG. 1, the gel according to the present inventionhad superior hardness compared to gelatin and the pectin gel, similarelasticity to gelatin and was less brittle than either of the other twogels.

FIGS. 2 and 3 respectively show the variation of elasticity andbrittleness, hardness and adhesiveness with polysaccharide concentrationof the gel (w/v).

EXAMPLE 2

Co-Gelling of Corn Bran and Wheat Bran Extracts

1. An extract of corn bran was prepared as in steps 1-4 of Example 1.

2. Wheat bran was macerated in hot water (70°0 C.) and hot water solublegums and starches removed by centrifugation at 2500 rpm for 15 minutesdiscarding the supernatants.

3. The pellet of insoluble material was resuspended in hot water (80°C.) and further centrifuged to remove soluble matter. This procedure wasrepeated until no more soluble matter was removed.

4. The remaining insoluble matter was suspended to 10% w/v in 2% KOH andstirred gently at 65°-80° C. for 2-3 hours, after which insolublematerial was removed by centrifugation at 2500 rpm for 20 minutes.

5. The supernatant was neutralised with acid (hydrochloric or citric)and dialysed against running water for 2 days.

6. The extract obtained from steps 1-5 and the corn bran extractobtained from steps 1-4 of Example 1 were mixed so as to give a solutioncontaining wheat bran extract at 2.0% w/v and corn bran extract at 0.5%w/v. To 100 ml of this mixture as added 1 ml of 100 micrograms/mlhorseradish peroxidase with mixing, followed by 0.5 ml hydrogen peroxideat 40 micrograms H₂ O₂ /ml. After mixing the solution was left to setfor 5-15 minutes at room temperature, for 1-2 minutes at 40° C. or forless than one minute at 50° C.

In contrast, neither the 2.0% wheat bran nor the 0.5% corn bran extractsdescribed above would form a firm gel when used alone.

EXAMPLE 3

Purification of Corn Bran Extract

An extract of corn bran prepared as in steps 1-4 of Example 1 waspurified as follows:

1. Neutralisation

The extract was neutralised with hydrochloric acid to pH 6-6.5 anddiluted to about 1.5% dry matter with water.

2. Salt Removal (Optional)

The extract was desalted by dialysis against running water for 3 days.Alternatively this step may involve tangential flow ultrafiltration.

3. Separation

The extract was then passed through a column containing activated carbonat a rate of 2-4 bed volumes per hour until the capacity of the columnwas exhausted. An eluate which was substantially free of mono andoligosaccharides, free ferulic and diferulic acids, and other organiccompounds which contribute to colour and odour, was obtained.

4. Concentration

The eluate was concentrated by precipitation with ammonium sulphate(other precipitating reagents such as ethanol, IMS propan-2-ol ormethanol could have been used). Alternatively the concentration couldhave been carried out by drying (spray or vacuum rotary drying) andredissolving of the eluate.

5. Precipitation

The redissolved precipitate produced in stage 4 was subjected to alcoholprecipitation by adding 2.8 volume of alcohol.

6. Peroxide Treatment

The redissolved precipitate was added to water to produce a gellingmedium of hemicellulosic concentration between 0.5 and 3.0% w/v. 30-100micromoles of peroxide per gram of the polysaccharide and 100-200microgram of peroxidase enzyme were added to the medium.

The above purification process could similarly be applied to wheatbranextract.

EXAMPLE 4

The presence of diferulate cross-links in a gel material according tothe present invention was investigated spectrophotometrically.

It can be seen with reference to the ultra-violet spectrum shown in FIG.4a that a characteristic absorbance peak was obtained for a 50 μMferulic acid solution at an excitation wavelength of about 320 nm.(Ferulic acid being known to have an absorbance peak at 320 nm,coefficient of extinction=15,100 for this peak, while diferulate showslittle absorbance at this wavelength). Conversely, with reference toFIG. 4b, no such characteristic absorbance peak was obtained at 320 nmfor a gel according to the present invention, thus confirming theabsence of ferulic acid residues from the gel.

It was found to be possible to investigate the extent of the diferulatecross-linking in the gel by correlating the UV absorbance of the gelagainst an ungelled polysaccharide having ferulic acid residues.

The correlation was achieved by measuring the uv absorbance of the gelat 320 nm, against the absorbance of the ungelled polysaccharide at thesame wavelength. FIG. 5 shows the negative absorbance peak obtained, theextent of diferulate cross-linking was estimated from the negative peak.

EXAMPLE 5

The diferulate cross-linking was further investigated by infra-redspectrophotometry.

Substituted aromatic acids have many characteristic bands of absorbancebetween wave numbers 1480 and 1700 cm⁻¹ and between wave numbers 1000and 1250 cm⁻¹.

The appearance of additional peaks of absorbance at about 1550-1600 cm⁻¹and at around 1100-1160 cm⁻¹ is characteristic of substituted biphenylgroups and is indicative of the formation of diferulate.

It can be seen from comparisons of FIG. 6a (an infra-red spectrum of anungelled polysaccharide) and FIG. 6b (an infra-red spectrum of a gelaccording to the present invention) that there are additional absorbancepeaks in the wavelength region 1550 to 1600 cm⁻¹, and 1100-1160 cm⁻¹.The additional peaks were attributed to the presence of diferulatecross-links as discussed above.

We claim:
 1. A gel material obtained from a starch-free water-solublehemicellulosic material derived from American corn bran Zea mays, whichgel material is free of glucans and pectins and comprises apolysaccharide network which comprises:(i) a matrix of polysaccharidechains; and (ii) a multiplicity of ferulate bridges cross-linking saidpolysaccharide chains at regular intervals along said polysaccharidechains, said gel material having infra-red absorbances in the wavelengthrange of 1550-1600 cm⁻¹ and in the wavelength range of 1100-1160 cm⁻¹.2. A gel material according to claim 1, wherein said polysaccharidechains contain about 10% to about 20% arabinoxylan and/orglucuronoarabinoxylan moieties.
 3. A gel material according to claim 1,having a molecular weight in the range of 80 to 600 kdaltons.
 4. A gelmaterial according to claim 1, which contains one or more metal cationsselected from the group consisting of Ca²⁺, Cu²⁺, Zn²⁺, Fe³⁺ and Al³⁺.5. A method of producing a gel material, which method comprises:(a)providing a starch-free starting medium derived from American corn branZea mays and comprising a water soluble hemicellulosic material which isfree of glucans; (b) extracting said hemicellulosic material with anon-acidic aqueous reagent; and (c) reacting the extractedhemicellulosic material with an oxidizing system comprising a peroxide,together with an oxygenase, so as to produce a gel material whichcomprises a matrix of polysaccharide chains, and a multiplicity offerulate bridges cross-linking said polysaccharide chains at regularintervals along said polysaccharide chains.
 6. A method according toclaim 5, wherein the starting medium in step (a) is in a ground form. 7.A method according to claim 6, wherein the ground starting medium isenzyme treated, air classified or sieved to remove starch prior to step(b).
 8. A method according to claim 7, wherein the enzyme treatmentcomprises treatment with an enzyme selected from the group consisting ofalpha-amylase, beta-amylase or a mixture thereof.
 9. A method accordingto claim 5, wherein the glucans have been removed from the startingmedium by enzyme digestion with a carbohydrase enzyme.
 10. A methodaccording to claim 5, wherein the non-acidic aqueous reagent of step (b)is an alkali selected from the group consisting of NaOH and KOH.
 11. Amethod according to claim 10, wherein the alkali is used in an amount of0.1% to 10% by weight of said aqueous reagent for a time of from 20minutes to 5 hours.
 12. A method according to claim 11, wherein thealkali is used in an amount of 0.5 to 2.5% by weight of said aqueousreagent for about 2 hours.
 13. A method according to claim 10, whereinthe extraction of step (b) is carried out at a temperature of from 30°C. to 100° C.
 14. A method according to claim 5, wherein the extractionof step (b) is carried out with water at a temperature of 50° C. to 80°C. for 0.5 to 2 hours.
 15. A method according to claim 5, whichcomprises treatment with an acid and precipitation with an alcoholfollowing step (b) and prior to step (c).
 16. A method according toclaim 15, wherein the acid is acetic acid.
 17. A method according toclaim 5, wherein the resulting gel material is dried.
 18. A methodaccording to claim 15, wherein the alcohol is ethanol.
 19. A methodaccording to claim 18, wherein the alcohol is added in an amount of from1.5 to 3.5 volumes.
 20. A method according to claim 5, wherein thehemicellulosic material which is extracted in step (b) is then passedthrough an activated carbon column prior to step (c) to produce apurified hemicellulosic material.
 21. A method according to claim 20,wherein said purified hemicellulosic material is precipitated withammonium sulfate, methanol, ethanol or iso-propanol prior to step (c) toproduce a concentrated, purified hemicellulosic material.
 22. A methodaccording to claim 21, wherein the salt content of said concentrated,purified hemicellulosic material is lowered by dialysis or tangentialflow ultrafiltration prior to step (c).
 23. A method according to claim5, wherein the oxygenase comprises a peroxidase.
 24. A method accordingto claim 23, wherein the peroxidase comprises horseradish peroxidase.25. A method according to claim 5, wherein the peroxide compriseshydrogen peroxide.
 26. A method according to claim 5, which furthercomprises the addition of polyvalent metal cations to said startingmedium of step (a) or to said extracted hemicellulosic material of step(b) prior to step (c).
 27. A method according to claim 26, wherein saidpolyvalent metal cations are selected from the group consisting of Ca²⁺,Cu²⁺, Zn²⁺, Fe³⁺ and Al³⁺.
 28. A gel material produced by the method ofclaim
 5. 29. A wound dressing having a surface for contact with a wound,said surface comprising a gel material according to claim
 1. 30. A wounddressing according to claim 29, which consists essentially of said gelmaterial.
 31. A method for treatment of wounds, which comprises applyingthereto the gel material of claim 1.